Move WikiPageIniItem to core.

Moves the WikiPageIniItem to the main repo so I can use it in the about plugin.  Mostly copy paste, except adding the `_sr` property to `GoldPartner` and `GoldFeature` 

see https://github.com/reddit/reddit-public/pull/2347

:eyeglasses: @Deimos @spladug 
Shouldn't be any need to import `WikiPage` any more, just `WikiPageIniItem`.